rfc9744v1.txt   rfc9744.txt 
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Nokia Nokia
February 2025 February 2025
EVPN Virtual Private Wire Service (VPWS) Flexible Cross-Connect (FXC) EVPN Virtual Private Wire Service (VPWS) Flexible Cross-Connect (FXC)
Service Service
Abstract Abstract
This document describes a new EVPN Virtual Private Wire Service This document describes a new EVPN Virtual Private Wire Service
(VPWS) service type specifically for multiplexing multiple attachment (VPWS) service type specifically for multiplexing multiple attachment
circuits across different Ethernet Segments and physical interfaces circuits across different Ethernet Segments (ESs) and physical
into a single EVPN VPWS service tunnel and still providing Single- interfaces into a single EVPN-VPWS service tunnel and still providing
Active and All-Active multi-homing. This new service is referred to Single-Active and All-Active multi-homing. This new service is
as the EVPN VPWS Flexible Cross-Connect (FXC) service. This document referred to as the EVPN-VPWS Flexible Cross-Connect (FXC) service.
specifies a solution based on extensions to EVPN VPWS (RFC 8214), This document specifies a solution based on extensions to EVPN-VPWS
which in turn is based on extensions to EVPN (RFC 7432). Therefore, (RFC 8214), which in turn is based on extensions to EVPN (RFC 7432).
a thorough understanding of RFCs 7432 and 8214 are prerequisites for Therefore, a thorough understanding of RFCs 7432 and 8214 are
this document. prerequisites for this document.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841. Internet Standards is available in Section 2 of RFC 7841.
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in the Revised BSD License. in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction 1. Introduction
1.1. Terminology 1.1. Terminology
1.2. Requirements Language 1.2. Requirements Language
2. Requirements 2. Requirements
3. Solution 3. Solution
3.1. VPWS Service Identifiers 3.1. VPWS Service Identifiers
3.2. Default Flexible Xconnect 3.2. Default Flexible Cross-Connect
3.2.1. Multi-homing 3.2.1. Multi-homing
3.3. VLAN-Signaled Flexible Xconnect 3.3. VLAN-Signaled FXC
3.3.1. Local Switching 3.3.1. Local Switching
3.4. Service Instantiation 3.4. Service Instantiation
4. BGP Extensions 4. BGP Extensions
5. Failure Scenarios 5. Failure Scenarios
5.1. EVPN VPWS Service Failure 5.1. EVPN-VPWS Service Failure
5.2. Attachment Circuit Failure 5.2. Attachment Circuit Failure
5.3. PE Port Failure 5.3. PE Port Failure
5.4. PE Node Failure 5.4. PE Node Failure
6. Security Considerations 6. Security Considerations
7. IANA Considerations 7. IANA Considerations
8. References 8. References
8.1. Normative References 8.1. Normative References
8.2. Informative References 8.2. Informative References
Contributors Contributors
Authors' Addresses Authors' Addresses
1. Introduction 1. Introduction
[RFC8214] describes a solution to deliver point-to-point (P2P) [RFC8214] describes a solution to deliver point-to-point (P2P)
services using BGP constructs defined in [RFC7432]. It delivers this services using BGP constructs defined in [RFC7432]. It delivers this
P2P service between a pair of Attachment Circuits (ACs), where an AC P2P service between a pair of Attachment Circuits (ACs), where an AC
can designate on a Provider Edge (PE), a port, a VLAN on a port, or a on a PE can represent a port, a VLAN on a port, or a group of VLANs
group of VLANs on a port. It also leverages multi-homing and fast on a port. It also leverages multi-homing and fast convergence
convergence capabilities of [RFC7432] in delivering these VPWS capabilities of [RFC7432] in delivering these VPWS services. Multi-
services. Multi-homing capabilities include the support of single- homing capabilities include the support of Single-Active and All-
active and all-active redundancy mode, and fast convergence is Active redundancy mode, and fast convergence is provided using a
provided using a "mass withdrawal" message in control plane and fast "mass withdrawal" message in control plane and fast protection
protection switching using prefix-independent convergence in a data switching using prefix-independent convergence in a data plane upon
plane upon node or link failure [BGP-PIC]. Furthermore, the use of node or link failure [BGP-PIC]. Furthermore, the use of EVPN BGP
EVPN BGP constructs eliminates the need for multi-segment pseudowire constructs eliminates the need for multi-segment pseudowire auto-
auto-discovery and signaling if the VPWS service need to span across discovery and signaling if the VPWS service need to span across
multiple Autonomous Systems (ASes) [RFC5659]. multiple Autonomous Systems (ASes) [RFC5659].
Service providers have a very large number of ACs (in millions) that Service providers have a very large number of ACs (in millions) that
need to be backhauled across their MPLS/IP network. These ACs may or need to be backhauled across their MPLS/IP network. These ACs may or
may not require tag manipulation (e.g., VLAN translation). These may not require tag manipulation (e.g., VLAN translation). These
service providers want to multiplex a large number of ACs across service providers want to multiplex a large number of ACs across
several physical interfaces spread across one or more PEs (e.g., several physical interfaces spread across one or more PEs (e.g.,
several Ethernet Segments) onto a single VPWS service tunnel in order several ESs) onto a single VPWS service tunnel in order to a) reduce
to a) reduce the number of EVPN service labels associated with EVPN- the number of EVPN service labels associated with EVPN-VPWS service
VPWS service tunnels and thus the associated Operations, tunnels and thus the associated Operations, Administration, and
Administration, and Maintenance (OAM) monitoring and b) reduce EVPN Maintenance (OAM) monitoring and b) reduce EVPN BGP signaling (e.g.,
BGP signaling (e.g., not to signal each AC as it is the case in not to signal each AC as it is the case in [RFC8214]).
[RFC8214]).
Service providers want the above functionality without sacrificing Service providers want the above functionality without sacrificing
any of the capabilities of [RFC8214] including single-active and all- any of the capabilities of [RFC8214] including Single-Active and All-
active multi-homing and fast convergence. Active multi-homing and fast convergence.
This document specifies a solution based on extensions to EVPN VPWS This document specifies a solution based on extensions to EVPN-VPWS
[RFC8214] to meet the above requirements. Furthermore, [RFC8214] is [RFC8214] to meet the above requirements. Furthermore, [RFC8214] is
itself based on extensions to EVPN [RFC7432]. Therefore, a thorough itself based on extensions to EVPN [RFC7432]. Therefore, a thorough
understanding of [RFC7432] and [RFC8214] are prerequisites for this understanding of [RFC7432] and [RFC8214] are prerequisites for this
document. document.
1.1. Terminology 1.1. Terminology
AC: Attachment Circuit AC: Attachment Circuit
ES: Ethernet Segment ES: Ethernet Segment
ESI: Ethernet Segment Identifier ESI: Ethernet Segment Identifier
EVI: EVPN Instance Identifier EVI: EVPN Instance Identifier
EVPN: Ethernet Virtual Private Network EVPN: Ethernet Virtual Private Network
Ethernet A-D: Ethernet Auto-Discovery per EVI and Ethernet A-D per Ethernet A-D: Ethernet Auto-Discovery (per EVI or per Ethernet A-D
ESI routes, as defined in [RFC7432] and [RFC8214]. per ESI routes, as defined in [RFC7432] and [RFC8214])
FXC: Flexible Cross Connect FXC: Flexible Cross-Connect
MAC: Media Access Control MAC: Media Access Control
MPLS: Multiprotocol Label Switching MPLS: Multiprotocol Label Switching
OAM: Operations, Administration, and Maintenance OAM: Operations, Administration, and Maintenance
PE: Provider Edge device PE: Provider Edge
VCCV: Virtual Circuit Connection Verification VCCV: Virtual Circuit Connectivity Verification
VID: VLAN ID VID: VLAN ID
VPWS: Virtual Private Wire Service VPWS: Virtual Private Wire Service
VRF: VPN Routing and Forwarding table VRF: VPN Routing and Forwarding
IP-VRF: VPN Routing and Forwarding table, for IP lookup IP-VRF: VPN Routing and Forwarding for IP lookup
MAC-VRF: VPN Routing and Forwarding table, for MAC lookup MAC-VRF: VPN Routing and Forwarding for MAC lookup
VID-VRF: VPN Routing and Forwarding table, for Normalized VID lookup VID-VRF: VPN Routing and Forwarding for normalized VID lookup
VPWS Service Tunnel: It is represented by a pair of EVPN service VPWS Service Tunnel: It is represented by a pair of EVPN service
labels associated with a pair of endpoints. Each label is labels associated with a pair of endpoints. Each label is
downstream assigned and advertised by the disposition PE through downstream assigned and advertised by the disposition PE through
an Ethernet A-D per EVI route. The downstream label identifies an Ethernet A-D per EVI route. The downstream label identifies
the endpoint on the disposition PE. A VPWS service tunnel can be the endpoint on the disposition PE. A VPWS service tunnel can be
associated with many VPWS service identifiers where each associated with many VPWS service identifiers where each
identifier is a normalized VID. identifier is a normalized VID.
Single-Active Redundancy Mode: When a device or a network is multi- Single-Active Redundancy Mode: When a device or a network is multi-
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interfaces instead of having one VPWS service tunnel per AC and 2) to interfaces instead of having one VPWS service tunnel per AC and 2) to
reduce the signaling of ACs as much as possible. Besides these two reduce the signaling of ACs as much as possible. Besides these two
requirements, they also want the multi-homing and fast convergence requirements, they also want the multi-homing and fast convergence
capabilities of [RFC8214]. capabilities of [RFC8214].
In [RFC8214], a PE signals an AC indirectly by first associating that In [RFC8214], a PE signals an AC indirectly by first associating that
AC to a VPWS service tunnel (e.g., a VPWS service instance) and then AC to a VPWS service tunnel (e.g., a VPWS service instance) and then
signaling the VPWS service tunnel via an Ethernet A-D per EVI route signaling the VPWS service tunnel via an Ethernet A-D per EVI route
with the Ethernet Tag field set to a 24-bit VPWS service instance with the Ethernet Tag field set to a 24-bit VPWS service instance
identifier (which is unique within the EVI) and the ESI field set to identifier (which is unique within the EVI) and the ESI field set to
a 10-octet identifier of the Ethernet Segment corresponding to that a 10-octet identifier of the ES corresponding to that AC.
AC.
Therefore, a PE device that receives such EVPN routes can associate Therefore, a PE device that receives such EVPN routes can associate
the VPWS service tunnel to the remote Ethernet Segment using the ESI the VPWS service tunnel to the remote ES using the ESI field.
field. Additionally, when the remote ES fails and the PE receives Additionally, when the remote ES fails and the PE receives the "mass
the "mass withdrawal" message associated with the failed ES per withdrawal" message associated with the failed ES per [RFC7432], a PE
[RFC7432], a PE device can quickly update its BGP list of available device can quickly update its BGP list of available remote entries to
remote entries to invalidate all VPWS service tunnels sharing the ESI invalidate all VPWS service tunnels sharing the ESI field and achieve
field and achieve fast convergence for multi-homing scenarios. Even fast convergence for multi-homing scenarios. Even if fast
if fast convergence was not needed, there would still be a need for convergence was not needed, there would still be a need for signaling
signaling each AC failure (via its corresponding VPWS service tunnel) each AC failure (via its corresponding VPWS service tunnel)
associated with the failed ES so that the BGP path list for each of associated with the failed ES so that the BGP path list for each of
them gets updated accordingly and the packets are sent to a backup PE them gets updated accordingly and the packets are sent to a backup PE
(in case of single-active multi-homing) or to other PEs in the (in case of Single-Active multi-homing) or to other PEs in the
redundancy group (in case of all-active multi-homing). In the redundancy group (in case of All-Active multi-homing). In the
absence of updating the BGP path list, the traffic for that VPWS absence of updating the BGP path list, the traffic for that VPWS
service tunnel will be black-holed. service tunnel will be black-holed.
When a single VPWS service tunnel carries multiple ACs across various When a single VPWS service tunnel carries multiple ACs across various
Ethernet Segments (physical interfaces) without signaling the ACs via ESs (physical interfaces) without signaling the ACs via EVPN BGP to
EVPN BGP to remote PE devices, those remote PE devices lack the remote PE devices, those remote PE devices lack the information to
information to associate the received Ethernet Segment with these ACs associate the received ES with these ACs or with their local ACs.
or with their local ACs. They also lack the association between the They also lack the association between the VPWS service tunnel (e.g.,
VPWS service tunnel (e.g., EVPN service label) and the far-end ACs. EVPN service label) and the far-end ACs. This means that, while the
This means that, while the remote PEs can associate their local ACs remote PEs can associate their local ACs with the VPWS service
with the VPWS service tunnel, they cannot make similar associations tunnel, they cannot make similar associations for the far-end ACs.
for the far-end ACs.
Consequently, in case of a connectivity failure to the ES, the remote Consequently, in case of a connectivity failure to the ES, the remote
PEs are unable to redirect traffic via another multi-homing PE to PEs are unable to redirect traffic via another multi-homing PE to
that ES. In other words, even if an ES failure is signaled via EVPN that ES. In other words, even if an ES failure is signaled via EVPN
to the remote PE devices, they cannot effectively respond because to the remote PE devices, they cannot effectively respond because
they do not know the relationship between the remote ES, the remote they do not know the relationship between the remote ES, the remote
ACs, and the VPWS service tunnel. ACs, and the VPWS service tunnel.
To address this issue when multiplexing a large number of ACs onto a To address this issue when multiplexing a large number of ACs onto a
single VPWS service tunnel, two mechanisms have been developed: one single VPWS service tunnel, two mechanisms have been developed: one
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This waste of network resources during a connection failure may be This waste of network resources during a connection failure may be
transient, as it can be detected and prevented at the application transient, as it can be detected and prevented at the application
layer in certain cases. Section 3.2 outlines a solution for such layer in certain cases. Section 3.2 outlines a solution for such
single-homing VPWS services. single-homing VPWS services.
For VPWS services where one of the endpoints is multi-homed, there For VPWS services where one of the endpoints is multi-homed, there
are two options: are two options:
1. Signal each AC via BGP, allowing the path list to be updated upon 1. Signal each AC via BGP, allowing the path list to be updated upon
a failure affecting those ACs. This solution is described in a failure affecting those ACs. This solution is described in
Section 3.3 and is referred to as the "VLAN-signaled flexible Section 3.3 and is referred to as the "VLAN-signaled FXC
cross-connect service". service".
2. Bundle several ACs on an ES together per destination endpoint 2. Bundle several ACs on an ES together per destination endpoint
(e.g., ES, MAC-VRF, etc.) and associate such a bundle with a (e.g., ES, MAC-VRF, etc.) and associate such a bundle with a
single VPWS service tunnel. This approach is similar to the single VPWS service tunnel. This approach is similar to the VLAN
VLAN-bundle service interface described in [RFC8214]. This bundle service interface described in [RFC8214]. This solution
solution is described in Section 3.2.1. is described in Section 3.2.1.
3. Solution 3. Solution
This section specifies how to provide a new VPWS service between two This section specifies how to provide a new VPWS service between two
PE devices where a large number of ACs (such as VLANs) that span PE devices where a large number of ACs (such as VLANs) that span
across multiple Ethernet Segments (physical interfaces) on each PE across multiple ESs (physical interfaces) on each PE are multiplexed
are multiplexed onto a single P2P EVPN service tunnel. Since the onto a single P2P EVPN service tunnel. Since the multiplexing
multiplexing involves several physical interfaces, there can be involves several physical interfaces, there can be overlapping VLAN
overlapping VLAN IDs (VIDs) across these interfaces. In such cases, IDs (VIDs) across these interfaces. In such cases, the VIDs must be
the VIDs must be translated into unique VIDs to prevent collisions. translated into unique VIDs to prevent collisions. Furthermore, if
Furthermore, if the number of VLANs being multiplexed onto a single the number of VLANs being multiplexed onto a single VPWS service
VPWS service tunnel exceeds 4095, then a single tag to double tag tunnel exceeds 4095, then a single tag to double tag translation must
translation must be performed. This translation of VIDs into unique be performed. This translation of VIDs into unique VIDs (either
VIDs (either single or double) results in a "Normalized VID". single or double) results in a "normalized VID".
When a single normalized VID is used, the lower 12 bits of the When a single normalized VID is used, the lower 12 bits of the
Ethernet Tag ID field in EVPN routes MUST be set to that VID. When a Ethernet Tag ID field in EVPN routes MUST be set to that VID. When a
double normalized VID is used, the lower 12 bits of the Ethernet Tag double normalized VID is used, the lower 12 bits of the Ethernet Tag
ID field MUST be set to the inner VID, while the higher 12 bits are ID field MUST be set to the inner VID, while the higher 12 bits are
set to the outer VID. As stated in [RFC8214], 12-bit and 24-bit VPWS set to the outer VID. 24-bit VPWS service instance identifiers
service instance identifiers representing normalized VIDs MUST be [RFC8214] as well as 12-bit VPWS service instance identifiers
right-aligned. representing normalized VIDs MUST be right-aligned.
Since there is only a single EVPN VPWS service tunnel associated with Since there is only a single EVPN-VPWS service tunnel associated with
many normalized VIDs (either single or double) across multiple many normalized VIDs (either single or double) across multiple
physical interfaces, an MPLS lookup at the disposition PE is no physical interfaces, an MPLS lookup at the disposition PE is no
longer sufficient to forward the packet to the correct egress longer sufficient to forward the packet to the correct egress
endpoint or interface. Therefore, in addition to an EVPN label endpoint or interface. Therefore, in addition to an EVPN label
lookup corresponding to the VPWS service tunnel, a VID lookup (either lookup corresponding to the VPWS service tunnel, a VID lookup (either
single or double) is also required. At the disposition PE, the EVPN single or double) is also required. At the disposition PE, the EVPN
label lookup identifies a VID-VRF, and the lookup of the normalized label lookup identifies a VID-VRF, and the lookup of the normalized
VIDs within that table identifies the appropriate egress endpoint or VIDs within that table identifies the appropriate egress endpoint or
interface. The tag manipulation (translation from normalized VIDs to interface. The tag manipulation (translation from normalized VIDs to
the local VID) SHOULD be performed either as part of the VID table the local VID) SHOULD be performed either as part of the VID table
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In [RFC8214], a unique value identifying the service is signaled in In [RFC8214], a unique value identifying the service is signaled in
the context of each PE's EVI. The 32-bit Ethernet Tag ID field MUST the context of each PE's EVI. The 32-bit Ethernet Tag ID field MUST
be set to this VPWS service instance identifier value. Translation be set to this VPWS service instance identifier value. Translation
at an Autonomous System Border Router (ASBR) is needed if re- at an Autonomous System Border Router (ASBR) is needed if re-
advertising to another AS affects uniqueness. advertising to another AS affects uniqueness.
For FXC, this same Ethernet Tag ID field value is an identifier that For FXC, this same Ethernet Tag ID field value is an identifier that
may represent: may represent:
* VLAN-Bundle Service Interface: a unique value for a group of VLANs * VLAN Bundle Service Interface: a unique value for a group of VLANs
* VLAN-Aware Bundle Service Interface: a unique value for individual * VLAN-Aware Bundle Service Interface: a unique value for individual
VLANs and is considered the same as the normalized VID VLANs and is considered the same as the normalized VID
Both the VPWS service instance identifier and normalized VID are Both the VPWS service instance identifier and normalized VID are
carried in the Ethernet Tag ID field of the Ethernet A-D per EVI carried in the Ethernet Tag ID field of the Ethernet A-D per EVI
route. For FXC, in the case of a 12-bit ID, the VPWS service route. For FXC, in the case of a 12-bit ID, the VPWS service
instance identifier is the same as the single-tag normalized VID and instance identifier is the same as the single-tag normalized VID and
will be the same on both VPWS service endpoints. Similarly in the will be the same on both VPWS service endpoints. Similarly in the
case of a 24-bit ID, the VPWS service instance identifier is the same case of a 24-bit ID, the VPWS service instance identifier is the same
as the double-tag normalized VID. as the double-tag normalized VID.
3.2. Default Flexible Xconnect 3.2. Default Flexible Cross-Connect
In this mode of operation, many ACs across several Ethernet Segments In this mode of operation, many ACs across several ESs are
are multiplexed into a single EVPN VPWS service tunnel represented by multiplexed into a single EVPN-VPWS service tunnel represented by a
a single VPWS service ID. This is the default mode of operation for single VPWS service ID. This is the default mode of operation for
FXC, and the participating PEs do not need to signal the VLANs FXC, and the participating PEs do not need to signal the VLANs
(normalized VIDs) in EVPN BGP. (normalized VIDs) in EVPN BGP.
Regarding the data plane aspects of this solution, the imposition PE Regarding the data plane aspects of this solution, the imposition PE
performs VID normalization, and the disposition PE carries out VID performs VID normalization, and the disposition PE carries out VID
lookup and translation. Both imposition and disposition PE devices lookup and translation. Both imposition and disposition PE devices
MUST be aware of the VLANs through configuration. There should MUST be aware of the VLANs through configuration. There should
ideally be a single point-to-point (P2P) EVPN VPWS service tunnel ideally be a single point-to-point (P2P) EVPN-VPWS service tunnel
between a pair of PEs for a specific set of ACs. between a pair of PEs for a specific set of ACs.
As previously mentioned, because the EVPN VPWS service tunnel is As previously mentioned, because the EVPN-VPWS service tunnel is
employed to multiplex ACs across various Ethernet Segments (ESs) or employed to multiplex ACs across various ESs or physical interfaces,
physical interfaces, the EVPN label alone is not sufficient for the EVPN label alone is not sufficient for accurate forwarding of the
accurate forwarding of the received packets over the MPLS/IP network received packets over the MPLS/IP network to egress interfaces.
to egress interfaces. Therefore, normalized VID lookup is REQUIRED Therefore, normalized VID lookup is REQUIRED in the disposition
in the disposition direction to forward packets to their proper direction to forward packets to their proper egress endpoints; the
egress endpoints; the EVPN label lookup identifies a VID-VRF, and a EVPN label lookup identifies a VID-VRF, and a subsequent normalized
subsequent normalized VID lookup in that table identifies the egress VID lookup in that table identifies the egress interface.
interface.
In this solution, for each PE, the single-homing ACs represented by In this solution, for each PE, the single-homing ACs represented by
their normalized VIDs are associated with a single VPWS service their normalized VIDs are associated with a single VPWS service
instance within a specific EVI. The generated EVPN route is an instance within a specific EVI. The generated EVPN route is an
Ethernet A-D per EVI route with an ESI of 0, the Ethernet Tag field Ethernet A-D per-EVI route with an ESI of 0, the Ethernet Tag field
is set to a VPWS service instance ID, and the MPLS label field is set is set to a VPWS service instance ID, and the MPLS label field is set
to a dynamically generated EVPN service label representing the EVPN to a dynamically generated EVPN service label representing the EVPN-
VPWS service tunnel. This route is sent with a Route Target (RT) VPWS service tunnel. This route is sent with a Route Target (RT)
that represents the EVI, which can be auto-generated from the EVI that represents the EVI, which can be auto-generated from the EVI
according to Section 5.1.2.1 of [RFC8365]. Additionally, this route according to Section 5.1.2.1 of [RFC8365]. Additionally, this route
is sent with the EVPN Layer 2 Extended Community defined in is sent with the EVPN Layer 2 Attributes Extended Community defined
Section 3.1 of [RFC8214] with two new flags (outlined in Section 4) in Section 3.1 of [RFC8214] with two new flags (outlined in
that indicate: 1) this VPWS service tunnel for the default Flexible Section 4) that indicate: 1) the VPW service tunnel (set to default
Cross-Connect and 2) the normalized VID type (single versus double). Flexible Cross-Connect) and 2) the normalized VID type (set to
The receiving PE uses these new flags for a consistency check and MAY normalized single VID or double VID). The receiving PE uses these
generate an alarm if it detects inconsistencies, but it will not new flags for a consistency check and MAY generate an alarm if it
disrupt the VPWS service. detects inconsistencies, but it will not disrupt the VPWS service.
It should be noted that in this mode of operation, a single Ethernet It should be noted that in this mode of operation, a single Ethernet
A-D per EVI route is transmitted upon the configuration of the first A-D per-EVI route is transmitted upon the configuration of the first
AC with the normalized VID. As additional ACs are configured and AC with the normalized VID. As additional ACs are configured and
associated with this EVPN VPWS service tunnel, the PE does not associated with this EVPN-VPWS service tunnel, the PE does not
advertise any additional EVPN BGP routes and only locally associates advertise any additional EVPN BGP routes and only locally associates
these ACs with the pre-established VPWS service tunnel. these ACs with the pre-established VPWS service tunnel.
3.2.1. Multi-homing 3.2.1. Multi-homing
The default FXC mode can also be used for multi-homing. In this The default FXC mode can also be used for multi-homing. In this
mode, a group of normalized VIDs representing ACs on a single mode, a group of normalized VIDs representing ACs on a single ES, all
Ethernet Segment, all destined to a single endpoint, are multiplexed destined to a single endpoint, are multiplexed into a single EVPN-
into a single EVPN VPWS service tunnel, which is identified by a VPWS service tunnel, which is identified by a unique VPWS service ID.
unique VPWS service ID. When employing the default FXC mode for When employing the default FXC mode for multi-homing, rather than
multi-homing, rather than using a single EVPN VPWS service tunnel, using a single EVPN-VPWS service tunnel, there may be multiple
there may be multiple service tunnels per pair of PEs. Specifically, service tunnels per pair of PEs. Specifically, there is one tunnel
there is one tunnel for each group of VIDs per pair of PEs, and there for each group of VIDs per pair of PEs, and there can be many such
can be many such groups between a pair of PEs, resulting in numerous groups between a pair of PEs, resulting in numerous EVPN service
EVPN service tunnels. tunnels.
3.3. VLAN-Signaled Flexible Xconnect 3.3. VLAN-Signaled FXC
In this mode of operation, similar to the default FXC mode described In this mode of operation, similar to the default FXC mode described
in Section 3.2, many normalized VIDs representing ACs across several in Section 3.2, many normalized VIDs representing ACs across several
Ethernet Segments and interfaces are multiplexed into a single EVPN ESs and interfaces are multiplexed into a single EVPN-VPWS service
VPWS service tunnel. However, this single tunnel is represented by tunnel. However, this single tunnel is represented by multiple VPWS
multiple VPWS service IDs (one per normalized VID), and these service IDs (one per normalized VID), and these normalized VIDs are
normalized VIDs are signaled using EVPN BGP. signaled using EVPN BGP.
In this solution, on each PE, the multi-homing ACs represented by In this solution, on each PE, the multi-homing ACs represented by
their normalized VIDs are configured with a single EVI. There is no their normalized VIDs are configured with a single EVI. There is no
need to configure a separate VPWS service instance ID in here, as it need to configure a separate VPWS service instance ID in here, as it
corresponds to the normalized VID. For each normalized VID on each corresponds to the normalized VID. For each normalized VID on each
Ethernet Segment, the PE generates an Ethernet A-D per EVI route ES, the PE generates an Ethernet A-D per-EVI route where the ESI
where the ESI field represents the ES ID, the Ethernet Tag field is field represents the ES ID, the Ethernet Tag field is set to the
set to the normalized VID, and the MPLS label field is set to a normalized VID, and the MPLS label field is set to a dynamically
dynamically generated EVPN label representing the P2P EVPN service generated EVPN label representing the P2P EVPN service tunnel. This
tunnel. This label is the same for all ACs multiplexed into a single label is the same for all ACs multiplexed into a single EVPN-VPWS
EVPN VPWS service tunnel. This route is sent with an RT representing service tunnel. This route is sent with an RT representing the EVI.
the EVI. As before, this RT can be auto-generated from the EVI per As before, this RT can be auto-generated from the EVI per
Section 5.1.2.1 of [RFC8365]. Additionally, this route includes the Section 5.1.2.1 of [RFC8365]. Additionally, this route includes the
EVPN Layer 2 Extended Community defined in Section 3.1 of [RFC8214] EVPN Layer 2 Attributes Extended Community defined in Section 3.1 of
with two new flags (outlined in Section 4) that indicate: 1) this [RFC8214] with two new flags (outlined in Section 4) that indicate:
VPWS service tunnel for VLAN-signaled Flexible Cross-Connect and 2) 1) this VPWS service tunnel for VLAN-signaled FXC and 2) the
the normalized VID type (single versus double). The receiving PE normalized VID type (single versus double). The receiving PE uses
uses these new flags for a consistency check and may generate an these new flags for a consistency check and may generate an alarm if
alarm if it detects inconsistency, but it will not disrupt the VPWS it detects inconsistency, but it will not disrupt the VPWS service.
service.
It should be noted that in this mode of operation, the PE sends a It should be noted that in this mode of operation, the PE sends a
single Ethernet A-D per EVI route for each AC that is configured. single Ethernet A-D per-EVI route for each AC that is configured.
Each normalized VID that is configured per ES results in generation Each normalized VID that is configured per ES results in generation
of an Ethernet A-D per EVI. of an Ethernet A-D per EVI.
This mode of operation enabled automatic cross-checking of normalized This mode of operation enabled automatic cross-checking of normalized
VIDs used for Ethernet Virtual Private Line (EVPL) services because VIDs used for Ethernet Virtual Private Line (EVPL) services because
these VIDs are signaled in EVPN BGP. For instance, if the same these VIDs are signaled in EVPN BGP. For instance, if the same
normalized VID is configured on three PE devices (instead of two) for normalized VID is configured on three PE devices (instead of two) for
the same EVI, then when a PE receives the second remote Ethernet A-D the same EVI, then when a PE receives the second remote Ethernet A-D
per EVI route, it generates an error message unless the two Ethernet per EVI route, it generates an error message unless the two Ethernet
A-D per EVI routes include the same ESI. Such cross-checking is not A-D per EVI routes include the same ESI. Such cross-checking is not
feasible in the default FXC mode because the normalized VIDs are not feasible in the default FXC mode because the normalized VIDs are not
signaled. signaled.
3.3.1. Local Switching 3.3.1. Local Switching
When cross-connection occurs between two ACs belonging to two multi- When cross-connection occurs between two ACs belonging to two multi-
homed Ethernet Segments on the same set of multi-homing PEs, the homed ESs on the same set of multi-homing PEs, the forwarding between
forwarding between the two ACs must be performed locally during the two ACs must be performed locally during normal operation (e.g.,
normal operation (e.g., in absence of a local link failure). This in absence of a local link failure). This means that traffic between
means that traffic between the two ACs MUST be locally switched the two ACs MUST be locally switched within the PE.
within the PE.
In terms of control plane processing, this means that when the In terms of control plane processing, this means that when the
receiving PE processes an Ethernet A-D per EVI route whose ESI is a receiving PE processes an Ethernet A-D per-EVI route whose ESI is a
local ESI, the PE does not modify its forwarding state based on the local ESI, the PE does not modify its forwarding state based on the
received route. This approach ensures that local switching takes received route. This approach ensures that local switching takes
precedence over forwarding via the MPLS/IP network. This method of precedence over forwarding via the MPLS/IP network. This method of
prioritizing locally switched traffic aligns with the baseline EVPN prioritizing locally switched traffic aligns with the baseline EVPN
principles described in [RFC7432], where locally switched preference principles described in [RFC7432], where locally switched preference
is specified for MAC/IP routes. is specified for MAC/IP routes.
In such scenarios, the Ethernet A-D per EVI route should be In such scenarios, the Ethernet A-D per-EVI route should be
advertised with the MPLS label either associated with the destination advertised with the MPLS label either associated with the destination
AC or with the destination Ethernet Segment in order to avoid any AC or with the destination ES in order to avoid any ambiguity in
ambiguity in forwarding. In other words, the MPLS label cannot forwarding. In other words, the MPLS label cannot represent the same
represent the same VID-VRF outlined in Section 3.3, as the same VID-VRF outlined in Section 3.3, as the same normalized VID can be
normalized VID can be reachable via two Ethernet Segments. In the reachable via two ESs. In the case of using an MPLS label per
case of using an MPLS label per destination AC, this approach can destination AC, this approach can also be applied to VLAN-based VPWS
also be applied to VLAN-based VPWS or VLAN-bundle VPWS services as or VLAN bundle VPWS services as per [RFC8214].
per [RFC8214].
3.4. Service Instantiation 3.4. Service Instantiation
The V field defined in Section 4 is OPTIONAL. However, if The V field defined in Section 4 is OPTIONAL. However, if
transmitted, its value may indicate an error condition that could transmitted, its value may indicate an error condition that could
lead to operational issues. In such cases, merely notifying the lead to operational issues. In such cases, merely notifying the
operator of an error is insufficient; the VPWS service tunnel must operator of an error is insufficient; the VPWS service tunnel must
not be established. not be established.
If both endpoints of a VPWS tunnel are signaling a matching If both endpoints of a VPWS tunnel are signaling a matching
Normalized VID in the control plane, but one is operating in single- normalized VID in the control plane, but one is operating in single-
tag mode and the other in double-tag mode, then the signaling of the tag mode and the other in double-tag mode, then the signaling of the
V-bit facilitates the detection and prevention of this tunnel's V-bit facilitates the detection and prevention of this tunnel's
instantiation. instantiation.
If single VID normalization is signaled in the Ethernet Tag ID field If single VID normalization is signaled in the Ethernet Tag ID field
(12 bits), yet the data plane is operating based on double tags, the (12 bits), yet the data plane is operating based on double tags, the
VID normalization applies only to the outer tag. Conversely, if VID normalization applies only to the outer tag. Conversely, if
double VID normalization is signaled in the Ethernet Tag ID field (24 double VID normalization is signaled in the Ethernet Tag ID field (24
bits), VID normalization applies to both the inner and outer tags. bits), VID normalization applies to both the inner and outer tags.
4. BGP Extensions 4. BGP Extensions
This document uses the EVPN Layer 2 attribute extended community as This document uses the EVPN Layer 2 Attributes Extended Community as
defined in [RFC8214] with two additional flags incorporated into this defined in [RFC8214] with two additional flags incorporated into this
Extended Community (EC) as detailed below. This EC is sent with Extended Community (EC) as detailed below. This EC is sent with
Ethernet A-D per EVI route per Section 3 and SHOULD be sent for both Ethernet A-D per-EVI route per Section 3 and SHOULD be sent for both
Single-Active and All-Active redundancy modes. Single-Active and All-Active redundancy modes.
+-------------------------------------------+ +-------------------------------------------+
| Type (0x06) / Sub-type (0x04) (2 octets) | | Type (0x06) / Sub-type (0x04) (2 octets) |
+-------------------------------------------+ +-------------------------------------------+
| Control Flags (2 octets) | | Control Flags (2 octets) |
+-------------------------------------------+ +-------------------------------------------+
| L2 MTU (2 octets) | | L2 MTU (2 octets) |
+-------------------------------------------+ +-------------------------------------------+
| Reserved (2 octets) | | Reserved (2 octets) |
skipping to change at line 554 skipping to change at line 547
Table 1 Table 1
The M and V fields are OPTIONAL. The M field is ignored at reception The M and V fields are OPTIONAL. The M field is ignored at reception
for forwarding purposes and is used for error notifications. for forwarding purposes and is used for error notifications.
5. Failure Scenarios 5. Failure Scenarios
The two following examples analyze the failure scenarios. The two following examples analyze the failure scenarios.
The first scenario is a default Flexible Xconnect with a multi-homing The first scenario is a default Flexible Cross-Connect with a multi-
solution, and it is depicted in Figure 1. In this case, VID homing solution, and it is depicted in Figure 1. In this case, VID
normalization is performed, and a single Ethernet A-D per EVI route normalization is performed, and a single Ethernet A-D per-EVI route
is sent for the bundle of ACs on an ES. That is, PE1 will advertise is sent for the bundle of ACs on an ES. That is, PE1 will advertise
two Ethernet A-D per EVI routes: The first one will identify the ACs two Ethernet A-D per-EVI routes: The first one will identify the ACs
on port p1's ES, and the second one will identify the AC2 in port on port p1's ES, and the second one will identify the AC2 in port
p2's ES. Similarly, PE2 will advertise two Ethernet A-D per EVI p2's ES. Similarly, PE2 will advertise two Ethernet A-D per-EVI
routes. routes.
N.VID 1,2,3 +---------------------+ N.VID 1,2,3 +---------------------+
PE1 | | PE1 | |
+---------+ IP/MPLS | +---------+ IP/MPLS |
+-----+ VID1 p1 | +-----+ | sv.T1 + +-----+ VID1 p1 | +-----+ | sv.T1 +
| CE1 |-------------| FXC |======+ PE3 +-----+ | CE1 |-------------| FXC |======+ PE3 +-----+
| | /\ | | | | \ +----------+ +--| CE3 | | | /\ | | | | \ +----------+ +--| CE3 |
+-----+\ +||---| | sv.T2 \ | | 1/ | | +-----+\ +||---| | sv.T2 \ | | 1/ | |
VID3\ / ||---| |=====+ \ | +-----+ | / +-----+ VID3\ / ||---| |=====+ \ | +-----+ | / +-----+
skipping to change at line 585 skipping to change at line 578
/ / \p3 | +-----+ sv.T3 / +====| | | +-----+ / / \p3 | +-----+ sv.T3 / +====| | | +-----+
VIDs1,2 / +----| FXC |=======+ / | | |---+ VIDs1,2 / +----| FXC |=======+ / | | |---+
+-----+ / /\ | | | | / | +-----+ |\3 +-----+ +-----+ / /\ | | | | / | +-----+ |\3 +-----+
| CE2 |-----||---| | | sv.T4 / | | \ | CE5 | | CE2 |-----||---| | | sv.T4 / | | \ | CE5 |
| |-----||---| | |======+ +----------+ +---| | | |-----||---| | |======+ +----------+ +---| |
+--VIDs3,4 \/ | +-----+ | | +-----+ +--VIDs3,4 \/ | +-----+ | | +-----+
p4 +---------+ | p4 +---------+ |
PE2 | | PE2 | |
N.VID 1,2,3 +-------------------+ N.VID 1,2,3 +-------------------+
Figure 1: Default Flexible Xconnect Figure 1: Default Flexible Cross-Connect
The second scenario, depicted in Figure 2, illustrates the VLAN- The second scenario, depicted in Figure 2, illustrates the VLAN-
signaled FXC mode with multi-homing. In this example: signaled FXC mode with multi-homing. In this example:
* CE1 is connected to PE1 and PE2 via (port,VID)=(p1,1) and (p3,3), * CE1 is connected to PE1 and PE2 via (port,VID)=(p1,1) and (p3,3),
respectively. CE1's VIDs are normalized to value 1 on both PEs, respectively. CE1's VIDs are normalized to value 1 on both PEs,
and CE1 is cross-connected to CE3's VID 1 at the remote end. and CE1 is cross-connected to CE3's VID 1 at the remote end.
* CE2 is connected to PE1 and PE2 via ports p2 and p4, respectively: * CE2 is connected to PE1 and PE2 via ports p2 and p4, respectively:
- The combinations (p2,1) and (p4,3) identify the ACs used to - The combinations (p2,1) and (p4,3) identify the ACs used to
cross-connect CE2 to CE4's VID 2 and are normalized to value 2. cross-connect CE2 to CE4's VID 2 and are normalized to value 2.
- The combinations (p2,2) and (p4,4) identify the ACs used to - The combinations (p2,2) and (p4,4) identify the ACs used to
cross-connect CE2 to CE5's VID 3 and are normalized to value 3. cross-connect CE2 to CE5's VID 3 and are normalized to value 3.
In this scenario, PE1 and PE2 advertise an Ethernet A-D per EVI route In this scenario, PE1 and PE2 advertise an Ethernet A-D per EVI route
for each normalized VID (values 1, 2, and 3). However, only two VPWS for each normalized VID (values 1, 2, and 3). However, only two VPWS
service tunnels are required: 1) VPWS Service Tunnel 1 (sv.T1) Service Tunnels are required: 1) VPWS Service Tunnel 1 (sv.T1)
between PE1's FXC service and PE3's FXC and 2) VPWS Service Tunnel 2 between PE1's FXC and PE3's FXC and 2) VPWS Service Tunnel 2 (sv.T2)
(sv.T2) between PE2's FXC and PE3's FXC. between PE2's FXC and PE3's FXC.
N.VID 1,2,3 +---------------------+ N.VID 1,2,3 +---------------------+
PE1 | | PE1 | |
+---------+ IP/MPLS | +---------+ IP/MPLS |
+-----+ VID1 p1 | +-----+ | + +-----+ VID1 p1 | +-----+ | +
| CE1 |------------| FXC | | sv.T1 PE3 +-----+ | CE1 |------------| FXC | | sv.T1 PE3 +-----+
| | /\ | | |=======+ +----------+ +--| CE3 | | | /\ | | |=======+ +----------+ +--| CE3 |
+-----+\ +||---| | | \ | | 1/ | | +-----+\ +||---| | | \ | | 1/ | |
VID3\ / ||---| | | \ | +-----+ | / +-----+ VID3\ / ||---| | | \ | +-----+ | / +-----+
\ / /\/ | +-----+ | +=====| FXC |----+ \ / /\/ | +-----+ | +=====| FXC |----+
skipping to change at line 630 skipping to change at line 623
/ / \p3 | +-----+ | / | | | | +-----+ / / \p3 | +-----+ | / | | | | +-----+
VIDs1,2 / +----| FXC | / | | |---+ VIDs1,2 / +----| FXC | / | | |---+
+-----+ / /\ | | |======+ | +-----+ |\3 +-----+ +-----+ / /\ | | |======+ | +-----+ |\3 +-----+
| CE2 |-----||-----| | | sv.T2 | | \ | CE5 | | CE2 |-----||-----| | | sv.T2 | | \ | CE5 |
| |-----||-----| | | +----------+ +---| | | |-----||-----| | | +----------+ +---| |
+-----+ \/ | +-----+ | | +-----+ +-----+ \/ | +-----+ | | +-----+
VIDs3,4 p4 +---------+ | VIDs3,4 p4 +---------+ |
PE2 | | PE2 | |
N.VID 1,2,3 +------------------+ N.VID 1,2,3 +------------------+
Figure 2: VLAN-Signaled Flexible Xconnect Figure 2: VLAN-Signaled FXC
5.1. EVPN VPWS Service Failure 5.1. EVPN-VPWS Service Failure
The failure detection of an EVPN VPWS service can be performed via The failure detection of an EVPN-VPWS service can be performed via
OAM mechanisms such as VCCV-BFD (Bidirectional Forwarding Detection OAM mechanisms such as Bidirectional Forwarding Detection (BFD) for
for the Pseudowire Virtual Circuit Connectivity Verification) the pseudowire Virtual Circuit Connectivity Verification (VCCV)
[RFC5885], and upon such failure detection, the switchover procedure [RFC5885], and upon such failure detection, the switch over procedure
to the backup Switching Provider Edge (S-PE) is the same as the one to the backup PE is the same as the one described above.
described above.
5.2. Attachment Circuit Failure 5.2. Attachment Circuit Failure
In the event of an AC failure, the VLAN-Signaled and default FXC In the event of an AC failure, the VLAN-Signaled and default FXC
modes exhibit distinct behaviors: modes exhibit distinct behaviors:
* Default FXC (Figure 1): In the default mode, a VLAN or AC failure * Default FXC (Figure 1): In the default mode, a VLAN or AC failure
is not signaled. Consequently, in case of an AC failure, such as is not signaled. Consequently, in case of an AC failure, such as
VID1 on CE2, there is nothing to prevent PE3 from directing VID1 on CE2, there is nothing to prevent PE3 from directing
traffic from CE4 to PE1, leading to a potential black hole. traffic from CE4 to PE1, leading to a potential black hole.
Application layer OAM may be utilized if per-VLAN fault Application layer OAM may be utilized if per-VLAN fault
propagation is necessary in this scenario. propagation is necessary in this scenario.
* VLAN-Signaled FXC (Figure 2): In the case of a VLAN or AC failure, * VLAN-Signaled FXC (Figure 2): In the case of a VLAN or AC failure,
such as VID1 on CE2, this triggers the withdrawal of the Ethernet such as VID1 on CE2, this triggers the withdrawal of the Ethernet
A-D per EVI route for the corresponding Normalized VID, A-D per-EVI route for the corresponding Normalized VID,
specifically Ethernet-Tag 2. Upon receiving the route withdrawal, specifically Ethernet-Tag 2. Upon receiving the route withdrawal,
PE3 will remove PE1 from its outgoing path list for traffic PE3 will remove PE1 from its outgoing path list for traffic
originating from CE4. originating from CE4.
5.3. PE Port Failure 5.3. PE Port Failure
In the event of a PE port failure, the failure will be signaled, and In the event of a PE port failure, the failure will be signaled, and
the other PE will assume forwarding in both scenarios: the other PE will assume forwarding in both scenarios:
* Default FXC (Figure 1): In the case of a port failure, such as p2, * Default FXC (Figure 1): In the case of a port failure, such as p2,
the route for Service Tunnel 2 (sv.T2) will be withdrawn. Upon the route for Service Tunnel 2 (sv.T2) will be withdrawn. Upon
receiving the fault notification, PE3 will remove PE1 from its receiving the fault notification, PE3 will remove PE1 from its
path list for traffic originating from CE4 and CE5. path list for traffic originating from CE4 and CE5.
* VLAN-Signaled FXC (Figure 2): A port failure, such as p2, triggers * VLAN-Signaled FXC (Figure 2): A port failure, such as p2, triggers
the withdrawal of the Ethernet A-D per EVI routes for Normalized the withdrawal of the Ethernet A-D per EVI routes for normalized
VIDs 2 and 3, along with the withdrawal of the Ethernet A-D per ES VIDs 2 and 3, along with the withdrawal of the Ethernet A-D per-ES
route for p2's ES. Upon receiving the fault notification, PE3 route for p2's ES. Upon receiving the fault notification, PE3
will remove PE1 from its path list for the traffic originating will remove PE1 from its path list for the traffic originating
from CE4 and CE5. from CE4 and CE5.
5.4. PE Node Failure 5.4. PE Node Failure
In the case of PE node failure, the operation is similar to the steps In the case of PE node failure, the operation is similar to the steps
described above, albeit that EVPN route withdrawals are performed by described above, albeit that EVPN route withdrawals are performed by
the route reflector instead of the PE. the route reflector instead of the PE.
 End of changes. 58 change blocks. 
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